DoS Attacks – Understanding & Avoiding Them

In October, a cyber attack on Internet provider Dyn made many web services and sites inaccessible, including several newscasters (Fox News, HBO, CNN, Weather Channel, etc.) and world-class sites Netflix, Paypal, Yelp, Starbucks, just to name a few.

This attack is considered the largest denial of service attack ever made. In order to better understand what happened, we will first of all recall some basic notions of Internet communications. We will continue by talking about botnets and their evolution, before we see the specifics of this recent attack. Finally, we will see how we can guard against such attacks.

Internet Communication Basics

Most Internet communications are of the client-server type. The Internet browser is often used as a “client” and sends requests to the server, asking it to display a Youtube video, for example.

Each server has its own IP address. When navigating on Google, for instance, the server that responds to our request may be different depending on our geographical location. This is made possible by using a Domain Name System (DNS).

These DNS servers will translate an address with the words “www.google.com” into an IP address. This notion is important for understanding the attack that targeted Dyn.

History of botnets

A “botnet” (combination of robot and network) is a network of computers infected by a virus, which turns them into passive entities that remain listening to future instructions. The person controlling the botnet can then send commands to his army of infected computers. For example, ask his robots to send spam or launch distributed denial of service attacks (DDoS). The distributed nature of this architecture makes detection of DDoS attacks difficult.

With the miniaturization and ever-decreasing cost of computing devices, more and more objects become “connected”. This creates an ever-growing network of printers, IP cameras and all kinds of objects that are connected to the web. All these devices are ultimately small computers, and like all computers, they are vulnerable to attacks.

Moreover, since few people take the time to configure these connected objects, most of them are configured with default passwords, making it even simpler for an attacker to compromise and infect them viruses.

We find ourselves in a situation where many objects connected to the Internet are infected by a virus. And these devices, like IP cameras, are constantly on, unlike our computers. During the most recent DDoS attack, this botnet managed to generate up to 1.2 Tb of data per second! This is a data rate equivalent to nearly 2,000 DVD-quality movies sent per second!

Why did this attack hurt so badly?

Denial of service attacks have traditionally targeted servers or websites of companies that are chosen either for activism (or hacktivism) reasons, or for the purpose of extorting money.

The reasons for this attack are not yet known, but what differs from previous ones is the target. For the first time, it was not site servers that were targeted, but the DNS servers of the Dyn company.

The sites of Twitter, Paypal and Netflix, for example, were fully functional. But by preventing us from knowing the address of the servers to connect, this attack made all these sites inaccessible.

How to defend against these attacks?

DDoS attacks often follow a well-established pattern. A first way to protect oneself therefore is to use systems that will detect the signatures of these attacks.

Another way to prevent is to implement redundancy on servers. By using load balancers, you can intelligently route traffic to multiple servers, improving the system’s resilience to high traffic flows.

But that’s not all! We also need to guard against infections, to prevent one of our systems from becoming a botnet member. To do this, you must first protect computers with antivirus software.

However, many connected devices are too simple to install an antivirus. It is therefore essential to analyze the inbound network traffic in your corporate network, both to detect known threats and zero-day vulnerabilities.

It is possible to further minimize the risk of infection of your systems by correlating and monitoring event logs, such as continuous network and systems monitoring, which is part of the services offered by ESI Technologies.

Finally, remember to keep systems updated, in order to mitigate the risk that known vulnerabilities can be exploited and use unique and complex passwords. Password management software exist to make your life easier.

A specialized information security firm such as ESI Technologies will be able to assist you in analyzing your needs and selecting the most effective and efficient solutions to mitigate the risks of botnet attacks on your systems.

Tommy Koorevaar, Security Advisor – ESI Technologies

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